Method and apparatus for laser marking objects

ABSTRACT

Embodiments of the present invention comprise an apparatus for laser marking individual objects with indicia at a marking station wherein a predetermined window exists during which each object can be marked as the objects are conveyed along at least one path at a predetermined speed, the apparatus comprising, at least first and second lasers positioned adjacent one or more paths configured to direct a laser beam onto the objects to mark the same with indicia as the objects pass through the marking station, with each of the first and second lasers marking alternate following objects as they pass through the marking station.

BACKGROUND OF THE INVENTION

The present invention relates to laser systems and particularly a methodand apparatus for laser marking objects at high speed.

It is known that food and medicinal products that are susceptible tospoilage or effectiveness often have a use by or expiration date that isprinted on the items themselves or on the packaging of the items so apurchaser or potential user of the goods can make a judgment of whetherthe product is current or outdated. This is particularly important forsome food products, which can become dangerous, with chicken eggs beinga prime example because of the threat of salmonella poisoning.

It is for that reason that eggs are commonly packed in cartons that haveexpiration dates printed on the carton. A problem with this type ofdating is that consumers often remove the eggs from a carton and putthem in a special holders of their refrigerator and therefore lose theimportant expiration date information. Although it is not believed to bea widespread practice, there have been instances where establishmentshave removed eggs from one printed carton and placed in another having alater expiration date which can lead to usage beyond the date by whichsalmonella bacteria can develop into a dangerous condition. While therehave been attempts to print expiration dates on the eggs themselves withink jet printing or other type of marking, the permanency of suchprinted information is suspect and can often be removed.

A particularly desirable way in which to mark eggs is to use a laser toetch an expiration date and other information on the shell of the eggwhich results in a permanent marking that cannot be removed from the eggitself. Such marking is described in a patent application entitledMETHOD AND APPARATUS FOR MARKING AN EGG WITH AN ADVERTISEMENT, AFRESHNESS DATE AND A TRACEABILITY CODE, having Ser. No. 11/333,580,filed Jan. 17, 2006, which is specifically incorporated by referenceherein.

Because billions of eggs are produced annually in the United Statesalone, marking even a fraction of such numbers of eggs is a formidableundertaking. A large majority of eggs sold in the United States areproduced in only a few hundred locations. At these locations, gradersystems clean, candle, grade and pack eggs in large volumes. High volumegrader systems generally have from two to six rows of eggs that areconveyed through the various stages of the grading system and cancurrently process up to 175,000 eggs an hour.

Since marking of eggs must be done during this grading process to beeconomical, it is necessary to mark the eggs very rapidly withoutslowing down the speed of operation of the grader system. Thus, themarking operation must necessarily occur within a very small time andphysical size window. Because of time and physical size constraints, theamount and complexity of indicia that can be marked on the eggs islimited, and the laser marking apparatus must be sized to fit in thegrader in a manner which does not interfere with the normal operation ofthe grader.

SUMMARY OF THE INVENTION

Embodiments of the present invention comprise an apparatus for lasermarking individual objects with indicia at a marking station wherein apredetermined window exists during which each object can be marked asthe objects are conveyed along at least one path at a predeterminedspeed, the apparatus comprising, at least first and second laserspositioned adjacent one or more paths configured to direct a laser beamonto the objects to mark the same with indicia as the objects passthrough the marking station, with each of the first and second lasersmarking alternate following objects as they pass through the markingstation.

Various embodiments of the invention also comprise a method of lasermarking individual objects while they travel along at least one paththrough a marking station at a preferably predetermined speed,comprising the steps of activating a first laser to begin marking afirst object when it enters the marking station and continuing to markthe object through a first predetermined time window within the station,activating a second laser to begin marking a successive object when itenters the marking station and continuing to mark the successive objectthrough a second predetermined time window within the station, the firstand second predetermined time windows overlapping with one another sothat both objects are being simultaneously marked for at least a portionof the length of the time windows.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an egg having graphical representationsrendered thereon using a laser apparatus according to the presentinvention, which egg has a traceability code, an expiration date, alarge pictorial representation of the word EGGFUSION with Logo featuresand a line of text indicating a fresh new way to advertise;

FIG. 2 is a plan view of a grader having apparatus embodying the presentinvention shown in two locations along the grader system;

FIG. 3 is a plan view of the preferred embodiment of the laser markingapparatus embodying the present invention;

FIG. 4 is a side view of the apparatus shown in FIG. 3;

FIG. 5 is an end view of the apparatus shown in FIGS. 3 and 4;

FIG. 6 is a side view of components of the apparatus shown in FIGS. 3-5,and particularly illustrating the laser generator and components fordirecting the generator laser beam to a galvanometer for directing thebeam upwardly to mark eggs;

FIG. 7 is a top view of a portion of the preferred embodiment of thelaser marking apparatus embodying the present invention, similar to FIG.3, but illustrating the protective plate having apertures in which lasertransmitting Germanium lenses are installed to keep debris and matterfrom falling on galvanometer scanning heads;

FIG. 8 is a perspective view of an alternative embodiment of a portionof the apparatus shown in FIGS. 3 and 4, and particularly illustrating aprotective plate interposed between the galvanometers and the eggs thatare conveyed above the plate together with air knives for preventingmaterial from dropping onto the galvanometers;

FIG. 9 is a side view illustrating the apparatus shown in FIGS. 3-5wherein a portion of the apparatus is shown in a retracted and tiltedposition;

FIG. 10 is a simplified view illustrating a portion of a grader systemconveying three eggs, together with two galvanometers and particularlyillustrating the arc of movement of the laser beams;

FIG. 11 is a graphic representation of a reclining Donald Duck that ismade by a plurality of vectors; and

FIG. 12 is a similar view as FIG. 11, but with the number of vectorsbeing reduced;

FIG. 13 is an enlargement of a portion of the representation shown inFIG. 11;

FIG. 14 is an enlargement of a portion of the representation shown inFIG. 12; and

FIG. 15 is an enlarged and simplified portion of the representationshown in FIG. 14.

PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

Embodiments of the present invention are directed to apparatus as wellas a method for laser marking objects as they pass through a markingstation, with the marking being carried out by lasers that are designedand configured to render graphic representations as the objects passthrough the marking station. While the objects may comprise manydifferent sizes and forms, and may be made of many different types ofmaterials, the objects that are of particular importance and are thesubject of the present invention are eggs produced by chickens.

Parenthetically, it should be understood that terms “marking” or“etching” as used herein is intended to mean that a laser is employed asa radiant energy source. The laser beam is applied to leave most of thearea of the eggshell unaffected so as to provide contrast between theunaffected areas and the marking. The laser beam ablates and melts theouter surface material from the egg shell. A significant benefit of theuse of laser marking is that brown eggs have etched indicia that is acontrasting white color, while white eggs have etched indicia that is acontrasting dark brown color. The structural integrity of the egg shellis not affected because the etching by the beam only affects the outerapproximately 50 to approximately 90 micrometers of the egg shell, whichis approximately 5% to approximately 8% of the thickness of the eggshell.

Of the billions of eggs that are produced every year, the vast majorityof them are produced in a rural facility, which often have hundreds ofthousands of chickens which collectively produce more than a millioneggs per day. These eggs are processed through grading systems thatwash, grade, candle and pack the eggs at the facility, and which arethen shipped to various destinations. The grading operation is carriedout by high speed graders, some of which can handle up to 175,000 eggsper hour.

For this type of production to be maintained, an egg marking apparatusand method must be highly efficient to mark such numbers of eggs as theyare processed through the grader. This is particularly true if asignificant amount of indicia, such as graphic representations, isdesired to be etched onto every egg. It may also be necessary to usemultiple lasers if several lines of graphical representations are placedon each egg, and particularly if there are several rows of eggs. Notonly that, if a complex graphical representation is marked on an egg,such as an intricate or extensive logo or design, for example, it isnecessary to process the graphical representations in a manner wherebythe graphic representation can be rendered on the egg with visualfidelity to the representation within the constraints of the physicaland time window that exists for each egg that passes through a markingstation.

More particularly, and referring to FIG. 1, an egg 20 has an upper line22 of graphic representation comprising text “A005 EXP 9/15”, which is atraceability code followed by an expiration date. A middle line 24contains a larger graphic representation of the word EGGFUSION with logofeatures and a bottom line 26 of text indicates a fresh new way toadvertise. Another larger graphic representation is shown in FIGS. 11-14which is a pictorial representation of the Disney® character Donald Duckthat will be described in connection with vector technology.

Two different laser marking apparatus, indicated generally at 30 and 32,are shown in connection with a system that includes a grader 34 in FIG.2. The grader 34 is positioned to receive eggs by a conveyor frombuildings where hens are located and these eggs input to the grader 34where they are candled, cleansed, graded and then transported by aconveying mechanism 36 where they are diverted at packing stations 38,40, 42, 44 and 46, where they are packed in cartons for shipping. Thetwo apparatus 30, 32 illustrated in FIG. 2 may represent alternatelocations for a marking apparatus or they both may be provided to handledifferent rows of eggs of a multi-row conveyor, for example. In thisregard, each of the apparatus 30, 32 shown in FIG. 2 are configured tomark two rows of eggs that are being moved through the grading system.

Since the movement of the eggs from the grader 34 is to the left,obviously the left marking apparatus 32 would not mark eggs that arediverted at packing stations 38, 40 and 42. Each of the apparatus 30, 32has the capability of handling two rows of eggs A and B as shown inFIGS. 3 and 4.

Each of the marking apparatus 30, 32 are shown in FIGS. 3-10 and havefour laser marking units, indicated generally at 50, for marking eggs inrow A and four laser marking units, indicated generally at 52, formarking eggs in row B. The rows are shown by the lines marked A and B inFIGS. 3 and 4, with the eggs 20 shown in FIG. 4. The eggs 20 are carriedby a conveyor indicated generally at 54 which has calipers 56 onopposite sides that hold the eggs as they are conveyed along a path ofmovement. The distance between successive eggs is defined as the pitch,which is preferably about 76 millimeters, but which can vary. In thisregard, the pitch is determined by the grader manufacturer, to whichlaser marking apparatus is installed to mark the eggs. It is highlydesirable not to slow the normal operation of the grader equipment,which conveys the eggs at a speed of up to about 1.1 meters per second.

At that speed, there is a time window of about 69 milliseconds for eachlaser marking unit to mark each successive egg that passes through themarking station, which means that 14 eggs are marked per second. In thisregard, a marking station is defined as the distance along the conveyinglines A and B wherein one or more of the laser marking units 50 and 52can mark eggs, it being understood that the laser beam that is emittedfrom the units can be moved within an arc 58 having a range of about 30to about 35 degrees as is generally indicated in FIG. 10. Thus, themarking station extends generally between the width of the apparatusdefined by outer surfaces 60 of a laser marking unit enclosure 62 asshown in FIGS. 3-5.

Turning now to the laser marking units 50, 52, and referring to FIG. 6,a laser generator 64 is mounted to a vertical structural support 66 thatin turn is connected to a horizontal support 68. The laser generator 64outputs a laser beam 70 that passes through a collimating and focusinglens 72, is then reflected off of mirror 74 and passes through a hollowsupport pipe 76 supported by a bracket 78 to a galvanometer scanninghead 80 that directs the beam 70 upwardly to mark the eggs 20 as theypass by.

The laser generator 64 is preferably a CO₂ laser having approximately amaximum of about 70 watts of power, but which can be adjusted downwardlyif desired. The galvanometer scanning head is preferably a SCANcube® 7scan head having a digital standard interface controlled by a RTC® PCinterface board or a PC independent RTC® SCANalone board as sold by theSCANLAB America, Inc. of Naperville, Ill. The scan head has a 7millimeter aperture, a beam displacement of 9.98 mm, a dynamicperformance tracking error of 0.14 msec, an optical performance skew ofless than 6 mrad, a step response time at 1% of full scale of 0.25 ms, atypical marking speed of 2.5 m/sec, a typical positioning speed of 12.0m/s and a typical good writing quality speed for single strokecharacters of 1 millimeter height of 900 cps.

As shown in FIGS. 3-5, each of the laser marking units 50, 52 is mountedin the cabinet 62, with the laser generators 64 associated with units 50being staggered relative to those associated with units 52 so moreefficiently use space and keep all of the units in as small of afootprint as possible. The power supplies for the laser generators 64are stored in a lower enclosure 82. A frame structure 84 has adjustablefeet 86 for leveling and adjusting the elevation of the apparatus on thefloor of an installation, and the frame structure has horizontal railmembers 88 which carry the enclosure 62 and enable it to be moved froman operating position shown in FIGS. 3-5 to a retracted position asshown in FIG. 9.

The retracting capability enables the laser control units to beseparated from the grader conveyor line 36 and serviced, withoutstopping the grader if necessary. Because of clearances, before it isretracted, it may be necessary to lower the galvanometer scanning heads80 and this is accomplished by having pivot connections 90 on each sideof the rear corner of the enclosure 62, and a tilt frame actuatorassembly 92 on the front that can tilt the entire enclosure 62 whichlowers the galvanometer scanning heads 80 so that the cabinet can bemoved away from the conveyor 36.

Another enclosure 94 is mounted on the frame structure 84 which includescontrol and operating equipment, including program logic controllers,computers that also include RTC® PC interface boards for controlling thegalvanometer scanning heads 80, modems for communicating with lap topcomputers as well as off site networking equipment that upload anddownload data relating to the operation of the equipment. The data filesthat define the graphic representations including those that providevector coordinate information are generally downloaded from off-sitenetworking, and the production information is uploaded for billing andother purposes. The computers are also interconnected with the computersystem associated with the grader 34 that provides washer environmentalinformation such as wash water temperature, rinse water temperature andwash water pH values. There are sensors that sense operatingtemperatures of the laser generators and of the galvanometer scanningheads 80, as well as current sensors for power supplies. Positionsensors are also provided so that the operating status of all importantmoving components are monitored. The temperature and humidity withineach of the enclosures is monitored.

An operator keyboard 96 and LCD display 98 are provided to enableon-site trouble shooting or maintenance work. However, during normaloperation, and because of the extent of the monitoring and reportingthat is done, the need for an on-site attendant is minimized for manytypes of maintenance work. If a problem arises, there are typicallyemployees at the production facility that oversee the grader 34operation among other activities that can use the keyboard 96 anddisplay 98 while communicating with off-site personnel knowledgeableabout the marking apparatus and rectify most problems. A laser markingunit power switch 100 is provided, as is an emergency stop switch 102.Because of the heat that is generated by the equipment, coupled withrelatively high ambient temperature and humidity in such productionfacilities, air conditioning units 104 are provided for each enclosure.A main power disconnect panel 106 is located on the end of theapparatus.

Because the galvanometer scanning heads 80 are located below the eggs20, there is a likelihood that some eggs will be cracked and leaking orwill otherwise be wet so that material will drop toward the galvanometerscanning heads 80 and impair their operation. To guard against suchoccurrences, a protective plate structure 110 shown in FIG. 7 isprovided. It has left and right mounting legs 112 that are mounted tothe frame members 88, and which carry horizontal support pipes 114, towhich a plate 116 is attached. The plate has circular apertures 118 thatare located above the galvanometer scanning heads 80 that have germaniumprotective lenses 119 covering the apertures so that matter from theeggs cannot pass through the apertures and fall onto the galvanometerscanning heads 80. The Germanium lenses are stronger than glass and havethe property of passing a laser beam without distortion. Alternatively,zinc selenide lenses can be used inasmuch as this composition alsopasses laser light. Because the Germanium lenses are relativelyexpensive, the size of the apertures 118 is preferably only large enoughso that the normal arc or range of movement of the laser beam can bemade. To further prevent matter from entering the galvanometer scanningheads 80, a protective lens 120 is provided over the output of eachhead, as is indicated in FIG. 10.

An alternative embodiment is shown in FIG. 8, which has rectangularapertures 118′ in the plate 116, with this embodiment having an airnozzle or knife 122 provided adjacent each aperture 118 that isconnected to an air supply 124 through a series of hoses such as thehose 126 which directs a current of air over the apertures which blowsdripping matter away so that it does not penetrate the apertures 118.Operation of the air knives 122 may be controlled by solenoid valves 128in the hoses 126. A compressed air supply of at least 40 PSI at 50 CFMpreferably powers the eight air knives 122 shown. Since the platestructure 110 is mounted to the stationary frame 84, the hoses 126 andother air supplying components should be separated from the lasermarking units and the enclosure 62 because the latter can be retractedfrom the conveyor 36 as previously described, and the plate structuredoes not move.

With regard to laser marking eggs, a more powerful laser does notnecessarily enable the speed to be increased. It takes time to transferenergy to get the right effect. For example, baking a potato generallytakes about 45 minutes, and using a more powerful oven may explode thepotato. There is also a power transfer function to an egg shell thatproduces the right effect on the egg. The laser generator is sometimesadjusted downwardly, so the maximum of 70 watts is not used. Wet eggsand soft eggs may require power nearer the upper value. Experience hasshown that time is more valuable than power in marking eggs. It is forthat reason that it is preferred to maximize the writing time of theparticular graphic being written to the full 138 millisecond window (or69 milliseconds for some of the lasers). The preferred optics producedby the lens 72 is 100 millimeters which produces width of the beam orspot size of about 0.3 millimeters. These optical characteristics alsoprovide good depth of focus effect, which means that the eggs need notbe the same size. Stated in other words, a 10 millimeter change causedby different size eggs does not matter because the focal point of thebeam accommodates for such differences.

During operation, there are four laser marking units 50 or 52 markingeggs in each row, and the four units mark the upper, middle and bottomlines as shown in the egg 20 in FIG. 1. When the conveyor 54 moves atthe speed of 1.1 meter per second, there is only about 69 millisecondsin which to mark each egg 20. As is evident from FIG. 1, the amount andsize of a graphic representation that is being marked in the upper andbottom lines 22 and 26 is less than that in the middle line 24, whichmay be quite complex such as shown in FIGS. 11-15. The present apparatususes two of laser marking units for marking the lines 22 and 26, and thetwo remaining lasers for marking the middle line on alternating eggs.This effectively doubles the time window from about 69 milliseconds toabout 138 milliseconds with each of the two units marking every otheregg. Using such an alternating procedure, more complex and extensivemarking can be carried out in the middle line 24. Whereas the lasermarking units 50 that mark the top and bottom lines 22 and 26 areoperated during the 69 millisecond window to mark every egg as it comesalong, the two laser marking units 50 that mark line 24 will eachoperate in 138 millisecond time windows which will overlapping with oneanother so that both laser marking units 50 will be simultaneouslymarking eggs for most of said 138 millisecond time window.

When an involved graphic representation is to be marked on an egg, it isaccomplished by mapping a plurality of vectors on a physical grid thathas a maximum size of about 20 millimeters by 40 millimeters. Referringto the graphic representation shown in FIG. 11, it is comprised of 572vectors, such as vector 130 which has a start point 132 and an end point134. Each of the start and end points have an X and a Y coordinate andeach vector is a straight line.

The start and stop coordinates for every vector have to be programmed.This is generally done with an automatic conversion tool from web imagesthat are used in various steps to produce a vector representation of theimage. CorelDRAW® can be used, for example, which will produce a vectorgraphic representation from a bit graphic representation. However, theeffectiveness of such tools may be sufficiently lacking that it isnecessary to manually render certain types of graphics to obtain theright style of the graphic. The graphics can be provided in a PostSciptformat, i.e., “pps” or “ps”. Also there is a vector based plot fileformat called a “.plt” that can be used.

Generally, as the graphic representation moves through the time andspatial window, all of the lines on the left third are preferablycompleted as the middle third is being rendered, and similarly themiddle third is rendered before the right third is rendered. Thisgenerally requires very long vectors to be segmented. The graphic isgenerally drawn from left to right, but the rendering is not strictlyrequired. However, it is not be possible to render a vector beginning atthe left edge of the graphic if most rendering is being performed at theright third of it. To achieve the above, the order of every vector mustbe programmed and becomes part of the electronic file of a graphicrepresentation. The programming is done so that all of the vectors arespecified consistent with these requirements.

Based on the fact that the eggs are moving at a predetermined speed andgalvanometer parameters are known and/or set, such as turning on andturning off delay times, repositioning times, positioning speed, and thefact that only 70 milliseconds are available, the marking or writingspeed is determined to render the image of the graphic based on thosecalculations and determine whether the representation can be effectivelyrendered. Since all of the vectors are known, together with the aboveparameters, it can be calculated at what speed the galvanometer scanninghead 80 must write to complete the representation. Through experience,it has been found that approximately 200 vectors can be rendered in the138 millisecond time window with acceptable quality. Because thephysical size of the window on the egg is 20 millimeters by 40millimeters, vectors can be removed without significantly detrimentallyaffecting the visual fidelity of the representation that is beingrendered. The marking speed is preferably within the range of 400-800bits per millisecond with an acceptable result being achieved at 800, agood result at 600 and a great result at 400. These units represent thecoordinate space of 16 by 16 (0-65535 bits) that cover the 20 by 40millimeter physical size of the window. the galvanometer scanning heads80 can scan the entire field of 65535 bits in 65 milliseconds at amarking speed of 1000. Based on the optics described above, a markingspeed of 1000 also translates to a distance of approximately 100millimeters per millisecond. The quality of the mark can be affected bythe quality of egg, so that a mark rendered on good eggs by the systemat a particular set of parameters may be good, while those on poor eggsmay not be.

Returning to FIG. 11, if all of the 572 vectors cannot be etched in theallotted time, the representation must be simplified by steps thatinclude vector thinning and raster scanning to try to simplify therepresentation while maintaining realistic visual fidelity of therepresentation.

Vector thinning involves a process for simplifying the representation byreducing the number of vectors using an algorithm that is based on theDouglas Ramer Peucker algorithm for line simplification andgeneralization, which is used in digital cartography. The method forremoving intermediate points, i.e., vectors, consists of joining the twoends of the line with a straight line, called the base line. Theperpendicular distances of all intermediate points from this base lineare then calculated. If all these distances are less than somepredefined tolerance, representing half the width of the graphic line atsource scale, these points may be discarded and the original line can berepresented by the base line. If any of the intermediate points falloutside the tolerance band, the line is split into two parts at thefurthest point and the process is repeatedly applied to the tworesulting parts.

Raster scanning involves rasterizing all of the vectors onto a fixedgrid that enables the determination of the existence of coincidentpoints, which is a process for removing redundant coordinates. Whenpoints of two vectors are coincident with one another, one is preferablyeliminated. The grid is defined and vectors are drawn on the grid fromlongest to smallest. If a new vector is drawn without changing any ofthe grid, that means it is on top of another, and the point or points ofcoincidence are removed by turning off the laser at those points. Thisis done by digital differential analysis. This raster thinningeliminates vector elements that provide no additional graphicsartifacts. It is not technically a graphics grid, but is an internalmemory grid. When vectors are rasterized from longest to smallest andwhen get to small vectors, if not shading new grid squares, then nothingis being added to the final rendering and they are eliminated.

The process uses a digital differential analysis process that is similarto that described in a publication entitled Digital DifferentialAnalyzer for Lines by Jon Kirwan, published athttp://users.easystreet.com/jkirwan/dda.html, copyright November, 1999,where there are a series of coordinates that make up a string of lines.This publication is specifically incorporated by reference herein. Ifredundant grid locations are already filled in, that portion of thevector is eliminated. The grid is preferably comprised of a 16×16 bitmatrix that is mapped to a 15×15 bit physical grid that lays out on a20×40 millimeter space on an egg. The physical grid therefore containsabout 65536 blocks. The grid shown in the upper right-hand corner ofFIG. 15 representatively illustrates the size of blocks of the grid.

Very short vectors and point or near-point artifacts can be also removedbecause they are not visible when rendered. Such a process together withother processes was used to reduce the number of vectors shown in FIG.11 from 572 vectors to 227 vectors shown in FIG. 12.

The processes are illustrated in FIGS. 11-14, wherein a portion 136 ofthe representation of FIG. 11 is shown in FIG. 13 that compares with asimilar portion 138 of the simplified representation of FIG. 14. Thelines of portion 138 from FIG. 14 are slightly different and simplifiedrelative to the portions 136 shown in FIG. 13, and an enlargement of thebox 140 of FIG. 14 is shown in FIG. 15.

An example of the vector thinning simplification is shown by comparingconnected vectors 142, 144, 146, 148, 150, 152 and 154 in FIG. 13, witha simplified version comprised of vectors 156, 158, 160 and 162 shown inFIG. 14. While these two versions look relatively dissimilar in theenlarged FIGS. 13 and 14, they are quite similar in effect when viewedin the boxes 136 and 138 of FIGS. 11 and 12.

An example of the raster scanning is represented by the enlargement ofbox 140 from FIG. 14, which is shown in FIG. 15. The rasterization ofvectors 164, 166 and 168 show that they overlap one another in the areathat is crosshatched. Therefore, addresses that represent duplicates areused to turn off the laser marking units at appropriate times so thatthe location is only marked once.

Given that a laser etched line has a discrete width, another techniquethat can be used is that if two lines that are crossing or are veryclose together, there can be over-burn because of the width aspect ofthe line. Therefore, vector boundaries can be compared with other vectorboundaries and thinning appropriately done. Given that it takes time toturn the laser on and off, there is a point of diminishing returns withthe complexity of a vector thinning process.

The galvanometer scanning heads 80 are controlled by the RTC® PCinterface boards which are programmed using a 16-bit coordinate system.To compensate for marking a moving product, that graphics are staged tothe far right, i.e., when the left end of the representation of FIG. 11,to “anticipate” etching a moving egg.

This cannot be done with the 16-bit coordinate system, so it is mappedinto a 15 bit physical window, which essentially halves the size of thecoordinate space. A correction matrix ignores coordinates that areoutside of the 15 bit space. So the graphic is positioned in virtualspace so that when the egg comes into the frame, the galvanometerscanning heads 80 is moved over to the edge and starts rendering theimage immediately.

This technique is necessary because the entire graphic must be sent tothe galvanometer system in a coordinate system. Without the virtualmapping, it would be necessary for the entire graphic to be within thephysical window before rendered could begin, which would dramaticallyreduce the time in which rendering could occur. This technique enablesthe system to render the graphic during the entire window, i.e., theentire time in which rendering can be done.

If this were completely in the real or principal coordinate system, thesystem cannot start rendering until the whole graphic is within thespatial window. The graphic is staged as far to the right as possiblewith respect to the coordinate system. So when the galvanometer scanninghead 80 is to start rendering, it will move to the right and move withthe egg so that when the egg comes into the real coordinate system, thegalvanometer scanning head 80 can be controlled to go to a physicalcoordinate, i.e. an edge in the physical space so that it can startrendering the graphic when it appears in the 15 bit coordinate space.

It may be highly desirable for embodiments of the present invention tomark multiple objects with different graphical representations. In theevent that eggs are being marked, it may be desired to have a carton ofa dozen eggs marked with 12 different graphical representations, i.e.,advertisements for 12 different products or messages. In such event, thecomplexity of the graphical representations may vary significantly. Fora complex representation, the marking speed may have to be increased toa relative maximum to complete the entire representation. The fastermarking speed will reduce the print contrast, and conversely a slowermarking speed will increase the print contrast. It is desirable to havethe greatest possible print contrast and therefore it is desirable tomark each graphical representation using the entire 69 or 138millisecond time window. Since each graphical representation iscontained in a separate file, the optimum marking speed for eachrepresentation is made to be part of the file, and the operatingparameters of the apparatus are thereby tuned or configured forutilizing the entire time window during marking. In the example ofhaving 12 different representations for a dozen eggs in a carton, theapparatus would likely have its operating characteristics change duringthe marking of each successive egg having a different representation.Such configuration flexibility optimizes the effectiveness and qualityof the marking operation.

While various embodiments of the present invention have been shown anddescribed, it should be understood that other modifications,substitutions and alternatives are apparent to one of ordinary skill inthe art. Such modifications, substitutions and alternatives can be madewithout departing from the spirit and scope of the invention, whichshould be determined from the appended claims.

Various features of the invention are set forth in the appended claims.

1. Apparatus for laser marking individual objects with indicia at amarking station wherein a predetermined window exists during which eachobject can be marked as the objects are conveyed along at least one pathat a predetermined speed, said apparatus comprising: at least first andsecond laser marking units positioned adjacent said at least one pathconfigured to direct a laser beam onto the objects to mark the same withindicia as the objects pass through the marking station; each of saidfirst and second laser marking units marking alternate following objectsas they pass through the marking station.
 2. Apparatus as defined inclaim 1 wherein the indicia marked by said first and second lasermarking units comprises one or more graphic representations. 3.Apparatus as defined in claim 1 wherein said predetermined windowcomprises a range of motion of a laser beam produced by each of saidfirst and second laser marking units and a predetermined maximum timeduration.
 4. Apparatus as defined in claim 3 wherein each of said firstand second laser marking units comprises a laser generator and agalvanometer scanning head configured to mark graphic representationsaccording to vector coordinate information, said apparatus furthercomprising a control system for reading digital files that define saidvector coordinate information for specific graphic representations thatsaid laser marking units mark on the objects.
 5. Apparatus as defined inclaim 4 wherein said digital files further define the order of markingby the laser marking unit so that downstream vectors are markedgenerally before upstream vectors.
 6. Apparatus as defined in claim 4wherein said digital files for specific graphic representations furtherdefine a predetermined marking speed of said galvanometer scanning headfor marking said specific graphic representation.
 7. Apparatus asdefined in claim 6 wherein said predetermined marking speed for markingobjects that are chicken eggs for maximum print contrast is determinedto be the slowest marking speed that can complete a specific graphicrepresentation within said predetermined maximum time duration. 8.Apparatus as defined in claim 5 wherein determining the order of markingvectors minimizes the distance from the end of one vector to the startof the next vector to be rendered.
 9. Apparatus as defined in claim 4said predetermined conveying speed is a maximum of at least about 66meters a minute.
 10. Apparatus as defined in claim 4 wherein each ofsaid laser generators is a Carbon Dioxide laser having up to about 70watts of power and produces a laser beam that produces a mark on anobject of about 0.3 millimeter width.
 11. Apparatus as defined in claim1 wherein said predetermined conveying speed is a maximum of at leastabout 66 meters per minute.
 12. Apparatus as defined in claim 1 whereinsaid graphic representations comprise text as well as pictorialrepresentations.
 13. Apparatus as defined in claim 1 wherein saidobjects are chicken eggs.
 14. Apparatus for laser marking individualchicken eggs while they travel along at least one path through an egggrading system, said apparatus comprising: at least a first enclosurefor housing a processor for controlling the operation of said apparatus,including memory for storing digital information defining variousgraphic representations; a plurality of laser marking units operativelyconnected to said processor and configured to mark at least two graphicrepresentations on eggs traveling along said at least one path; each ofsaid laser marking units further comprising; a generator for producing alaser beam at an output; a galvanometer scanning head positionedadjacent the path configured to receive said laser beam and direct itonto eggs as they travel along the path.
 15. Apparatus as defined inclaim 14 wherein said laser marking units are movable away from thepath.
 16. Apparatus as defined in claim 15 wherein said laser generatorsare mounted in a second enclosure, and said scanning head is mounted onan elongated support that extends from said enclosure and positions saidscanning head under the path.
 17. Apparatus as defined in claim 16wherein said elongated support has a central opening through which saidlaser beam travels from said generator to said scanning head. 18.Apparatus as defined in claim 14 further comprising a protective lens onsaid scanning heads and a lens protection plate extending over saidscanning heads and having openings directly above said lenses throughwhich said laser beams can pass from said scanning heads to the eggs.19. Apparatus as defined in claim 14 further comprising a Germanium lensin each of said openings through which said laser beams can pass fromsaid scanning heads to the eggs, while preventing matter from passingthrough said openings. 20-22. (canceled)
 23. A method of laser markingindividual objects while they travel along at least one path through amarking station at a preferably first predetermined speed, comprisingthe steps of: activating a first laser to begin marking a first objectwhen it enters the marking station and continuing to mark the objectthrough a first predetermined time window within the station; activatinga second laser to begin marking a successive object when it enters themarking station and continuing to mark the successive object through asecond predetermined time window within the station; the first andsecond predetermined time windows overlapping with one another so thatboth objects are being simultaneously marked for at least a portion ofthe length of said time windows. 24-37. (canceled)